The Emerald Triangle refers to a region in Northern California which is named due to it being the largest cannabis producing region in the United States and the world. Mendocino County, Humboldt County, and Trinity County are the three counties in Northern California that make up this region. Growers have been cultivating cannabis plants in this region since the 1960s (During San Franciscos Summer of Love), and many growers in Mendocino County today have estimated they make $1 billion a year from cultivating it. The industry exploded in the region with the passage of California Proposition 215 which legalized use of cannabis for medicinal purposes in California.